1. Field of the Invention
The present invention relates to a process for the preparation of a water-dispersible pulverulent disperse dye formulation by spray-drying, and to the formulation obtainable by the process and to its use for dyeing synthetic fiber material.
2. Brief Description of the Prior Art
Synthetic water-insoluble dyes, e.g. disperse dyes or vat dyes, are converted, for use in dyeing textiles from an aqueous liquor, into formulations which on simple addition to water, or stirring into water, give a finely dispersed dye suspension. The preparation of such readily dispersible dye formulations is also described as finishing.
Depending on whether pulverulent or liquid dye formulations are to be prepared, the assistants, i.e. dispersants, used in finishing have to conform to different requirements.
The dispersion process, i.e. the formation of the fine dye particles, can be carried out by milling an aqueous suspension in the presence of dispersants, with or without additional assistants, e.g. protective colloids, wetting agents and the like. In general, the dispersion process is carried out in conventional comminution equipment, e.g. ball mills or high-speed mills such as attrition mills, sand mills or bead mills, which contain glass balls, porcelain balls, steel balls, quartz sand or plastic beads as the grinding medium.
The dispersant is intended to increase the rate of dispersion during comminution and to prevent reagglomeration of the comminuted (dispersed) particles, and recrystallization to form large particles. In the case of the preparation of pulverulent formulations, the dispersant must stabilize the aqueous dispersion until the latter is converted to a dry state, for example by spray-drying, and must prevent agglomeration of the finely dispersed particles from occurring during the brief drying process and during the subsequent storage of the pulverulent formulation. The state of fine dispersion obtained on drying persists for a long time if the ratio of dispersed dye to the dispersant does not exceed a certain ratio.